Well, there have been professors on the train before, so she might have been alluding to that. For example, Lupin and Slughorn. Didn't seem too far of a stretch to me. Or, he could have been loading one of his own children on the train and just being bossy. If that were the case though, I think someone would have commented.

Far reach, but I wondered if Jo was wanting us to think of Professor McGonagall, as she taught the kids how to use their brooms. I'll have to re-read Year 1 and go to the scene where they learned to fly and see if any references.

Here's another -- I guess Harry never became an Auror, based on the comment that, "I've had enough trouble for a lifetime" . We just know he grew up to be a dad, which brought the story full circle, but as Harry continually talked about wanting to be an Auror that just seemed odd.